Geothermal stream ecosystems in a changing world

Background/Question/Methods

Due to an ever increasing demand for so called clean energy, geothermal areas around the globe are being utilized for power production in an increasing way with unforeseeable consequences. Geothermal ecosystems can without doubt be regarded as unique systems. The effluents from geothermal areas often harbor distinctive fauna and flora, which has solely evolved there, due to elevated temperatures and the unique chemical composition of the effluent waters. In Iceland, as well as in other countries where geothermal activity exists, geothermal areas have has been utilized for centuries. However, in recent decades due to an increasing demand for energy, there has been a drastic increase in exploiting geothermal systems. The effluent from geothermal power stations, not only leads to enhancing chemical concentration but also enhances temperature fluctuations, which are inevitably affecting the freshwater ecosystems which are receiving effluents due to power production. The main objective of the study was to assess the impact from geothermal utilization on stream ecosystems. Macroinvertebrates were collected from stream reaches which were above and below geothermal power station in North East Iceland. Nearby unaffected streams were used for comparison, as well as comparable unaffected geothermal streams within other geothermal areas.

Results/Conclusions

A significant difference was observed in the densities and diversities of macroinvertebrates between affected and unaffected streams within the same area. Similar results emerged when individual geothermal streams were compared. The dominant taxa in the geothermal streams were chironomids and simuliids. In the downstream reaches, below the geothermal power station, the fauna comprised only two or three species within the chironomid sub-family Orthocladiinae. The silica deposits below the geothermal power station affected the stream bed several kilometers downstream. However, the physical changes of the stream bed could only partially explain the decline in the densities and diversities of macroinvertebrates. Another significant cause for decrease in diversities and densities was due to drastic fluctuations in temperature. The results indicate the importance of discarding effluents from geothermal power stations, so they do not enter natural geothermal streams and destroy unique ecosystems which are sparse in the world.